Apparatus for elevating granular solids



Sept. 3, 1957 l. w. MILLS 2,305,102

APPARATUS FOR ELEVATING GRANULAR SOLIDS Filed Nov. 29, 1955 I4 I I8 Fig. 2 23 l2-- I9 l .-Ll I 257 I l8 I INVENTOR.

NOR W. MILLS ATTORNEY United States Patent M 2,805,102 APPARATUS FOR ELEVATING GRANULAR SOLIDS Ivor W. Mills, Glenolden, Pa., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Application November 29, 1955, Serial No. 549,633

3 Claims. (Cl. 302-53) This invention relates to apparatus for elevating granular solids by means of a lifting gas.

It is known in the art to elevate granular solids by suspending such solids in a lifting gas under pressure, and conveying the suspension upwardly through elongated confined lifting zones to a disengager zone in which space for expansion of the lifting gas is provided in order that the granular solids may be disengaged from the lifting gas and dropped into a lower portion of the disengaging zone.

Such lifting operations are beneficially applied in various processes, one important application involving the transportation of granular cracking catalyst as employed in the petroleum industry in the Houdriflow process, involving the gravitation of granular catalyst in compact form through a cracking or reaction zone and a catalyst regeneration zone in series, followed by pneumatic elevation of the cracking catalyst to a disengaging vessel positioned above the reaction zone. of operation is also applicable to other petroleum conversion processes, and also to processes outside the petroleum field.

It is also known in the art to provide a plurality of lift conduits in a single unit; such operation has important advantages, as known in the art, in that large volumetric fiow rates of granular solids can be obtained while using lift conduits having relatively small cross-sectional area. The use of lift conduits having small cross-sectional area provides a beneficial flow pattern in the lift conduit, with resulting reduction of attrition of the solids during the lifting operation.

Although the use of a plurality of lift conduits in a single unit has important advantages in the reduction of attrition of solids during the lifting operation, there is still a substantial amount of attrition which occurs during the lifting operation, and it would be highly desirable to further decrease the amount of attrition which occurs in the use of a plurality of lift conduits in a single unit, as well as in operations involving the use of a single lift conduit. The present invention provides a novel manner of reducing attrition of solids in pneumatic conveying systems involving single or multiple lift conduits.

According to the present invention, granular solids are classified according to particle size prior to the lifting operation, to obtain a plurality of portions of the solids to be elevated, each portion having a narrower range of particle size than the solids mass prior to the classification operation. At least one of the portions thus obtained is elevated separately from the other portions, with the result that in the elevating operation there are lesser amounts of certain sizes than in the case where the solids mass, without classification, is elevated through lift conduits in accordance with the practice of the prior art.

These changes in the particle size distribution of the solids elevated through an individual lift conduit produce beneficial results with regard to reduction of attrition. The reason for this reduction of attrition may be seen from the following considerations. When a mixture of granular solids having different particle size is elevated by means of a lifting gas through a lift conduit, the smaller size particles travel at a greater linear velocity, on the average, than the larger size particles. This discrepancy in velocity results in the smaller particles striking the larger particles from beneath duringthelifting This general scheme 2,805,102 Patented Sept. 3, 1957 operation. These contacts between the solid particles are an important factor contributing to the amount of attrition which occurs during the elevating operation.

The present invention, by eliminating certain sizes which would collide with particles of different size if allowed to remain, reduces the number of collisions which occur between particles during the lifting operation, with resulting decrease in the amountof attrition obtained.

The invention will be further described with respect to the attached drawing, in which Figure 2 is a schematic elevational view of a catalytic cracking system including a plurality of lift conduits for elevation of cracking catalyst, and in which Figure 1 is a sectional plan view of a lower portion of the apparatus illustrated in Figure 2. Referring to the drawing, there are shown therein a reactor vessel 10, a regenerator vessel 11, a solids classifier 12, a plurality of engager vessels 13, 14, 15 and 16, a plurality of lift conduits 17, 18, 19 and 20, and a disengager vessel 21. In operation, granular cracking catalyst is gravitated as a compact mass through the reactor vessel 10, wherein it is contacted with hydrocarbon cracking charge introduced through means not shown. The contacting is performed under cracking conditions, and the cracked products are removed from reactor 10 through means not shown. The catalyst, having carbonaceous materials deposited thereon as a result of the cracking operation, is gravitated through line 22 into regenerator 11, wherein it is contacted under combustion conditions with oxygen-containing gas introduced by means not shown. The flue gases produced in the regeneration are withdrawn from regenerator 11 through means not shown. The regenerated catalyst is withdrawn throughline 23 into classifier 12, which may be for ex ample a classifier of the shaking table type, as well known in the art.

During passage of the solids through classifier 12, separation of the particles according to particle size is continuously obtained, and a plurality of portions of the catalyst are withdrawn from the classifier through lines 24, 25, 26 and 27. The portion of solids withdrawn through line 27 has a smaller average particle size than the portion withdrawn through line 26, which in turn has smaller average particle size than the portion withdrawn through line 25, the portion withdrawn through line 24 having the greatest particle size of the four portions removed from classifier 12. Each of the separate portions obtained from classifier 12 has a narrower range of particle size than the solids mass introduced into classifier 12 through line 23.

Each of the four portions of solids obtained from classifier 12 is introduced into a dilferent engager vessel, the portion withdrawn through line 24 being introduced into vessel 13, the portion withdrawn through line 25 being introduced into engager 16, the portion withdrawn through line 26 being introduced into engager 14, and the portion withdrawn through line 27 being introduced into engager 15.

Lifting gas is introduced into the respective engaging vessels through lines 28, 29 and 30 and through an additional line, not shown, for introduction of lifting gas into engager 16. The lifting gas containing granular solids, introduced into the respective lifting gas streams in their respective engagers by conventional means, travels upwardly through the respective lift conduits, and thence into disengager 21. Solids are disengaged from each of the lifting gas streams and collected in the lower portion of disengager 21. Lifting gas from which the solids have been disengaged is withdrawn from disengager 21 through line 31. The granular solids recovered from each of the lifting gas streams are commingled and passed through line 32 into reactor vessel 10 to begin another cycle.

It is to be understood that the commingling of the various portions of granular solids prior to passage downwardly through the reactor and regenerator part of the system is not strictly necessary according to this embodiment of the invention, and thebenefits of the invention can be obtained in operation wherein the respective disengaged solids are passed downwardly through separate reactors and regenerators.

The apparatus according to the invention is applicable to mixtures of granular solids generally, a major proportion of which, prior to classification, is too large to pass through a 20 mesh U. S. Sieve series screen. The chemical nature of the solids may vary widely. The granular cracking catalyst to which the invention is particularly beneficially applied includes the 'well known synthetic silica-alumina cracking catalyst, activated clay catalyst, etc.

In the preceding description of the drawing, reference was made to apparatus involving the use of four lift paths, and the introduction of four different portions of classified solids into the respective lift paths. It is to be understood that the invention is applicable to any system involving the use of one or more lift paths. It is not necessary that the solids introduced into each lift path, in cases where more than two lift paths are employed, have a different range of particle size; it is necessary only that there be at least two different portions of the solids, which portions have different ranges of particle size. Thus, for example, the solids could be classified into two portions having different ranges of particle size, and one portion could be divided among one set of lift conduits, and the other portion divided among another set of lift conduits.

Any suitable classifying apparatus can be employed according to the present invention. The invention does not reside in the use of any particular type of classifying apparatus, but rather in the manner in which such apparatus is employed in combination with a system involving one or more lift paths; and therefore, conventional classifying apparatus, as well known in the art, can be employed.

Any suitable lifting gas can be employed in the process according to the invention. Various types of lifting gas are wellknown for use in elevation systems, and any of these is suitable for use according to the invention. Thus for example flue gas obtained in the regeneration operation of a catalytic cracking system can be used as a lifting gas, or steam, or air, etc.

As an example of operation according to the invention, the solids withdrawn from the regeneration may have the following approximate drstrrbutron of sizes:

Fraction Weight Passes Is Retained Percent '011 66 6 mesh. 4.5 6mesh Srnesh. 1. 9 8 mesh 10 mesh. 5. 7 10 mesh 12 mesh. 7. 5. 12 mesl1 14 mesh. 4. 6 14 mesh". 16 mesh. 9. 8 16 mesh.

Mesh sizes are given according to the U. S. Sieve Series.

The solids may be separated, for example, into two portions, one consisting of fraction 1 and the other of fractions 2 through 7. Fraction one can then be divided, without further classification according to size, to produce a total of three portions, two of which contain larger than 6 mesh particles, and the third of which con tains smaller than 6 mesh particles. The three portions may then be elevated separately through three lift conduits. In such operation, attrition is reduced since the larger than 6 mesh particles are not subject to the collisions with faster travelling, smaller than 6 mesh particles which would occur in conventional operation.

It is to be understood that division of the solids into larger numbers of portions having narrower ranges of particle size will produce even more pronounced reduction of attrition. However, the principle involved is illustrated in the specific example given, and the actual manner of division will depend on the characteristics of the particular operation involved, and can be determined in the light of the present specification by a person skilled in the art. t

in one specific embodiment of the invention, after classification of the solids according to size, one or more of the fractions of larger size is elevated together with one or more of the fractions of smaller size, the particles of intermediate size having in effect been removed prior to elevation. Thus, for'example, fraction 1 and a portion of fraction 7 of the above table could be elevated together through the same lift conduit or conduits, separately from fractions 2 to 6. Such operation is advantageous in that the-fine particles from-fraction 7 do not have sufiicient mass to cause excessive attrition by collisions with'the large particles in fraction 1; yet the suspension of those fine particles in lifting gas does pro vide a supporting medium for the large particles which has greater density than the lifting gas itself, and which is therefore capable of more efficiently elevating the large particles. i A

In such operation, the tines which are recombined with larger particles are preferably smaller than mesh in size, so that it would be preferred to further classify fraction 7 in order to remove the 16 to 5 mesh particles.

' It is to be understood that the various portions of solids obtained by classification can be recombined if desired, prior to elevation, in any suitable manner, rovidcd that the portion ultimately elevated has had removed therefrom particles which would otherwise have caused additional attrition as a result of collisions with other particles having difierent size.

The invention claimed is:

1. Apparatus for circulating granular solids which coinprises: means for passing granular solids repeatedly through a downflow system and through an upflow system comprising at least two separate elevating means; means for classifying granular solids according to particle size to obtain a plurality of portions at least one of which has a narrower range of particle size than the solids prior to classification; means for introducing a separate portion of the classified solids, having narrower range of particle size than the solids prior to classification, into a first elevating means of said upflow system; means for introducing lifting gas into the first elevating means; means for disengaging solids from lifting gas at the upper end of the first elevating means; means for introducing disengaged solids into the downfiow system; means for introducing another portion of the classified solids into a second elevating means of said upfiow system; and means for introducing solids from the second elevating means into the downfiow system.

2. Apparatus according to claim 1 and additionally comprising means for introducing lifting gas into the second elevating means, both elevating means communicating with said means for disengaging solids.

3'. Apparatus according to claim 1 wherein means are provided for classifying granular solids to obtain three fractions having different average particle size, and wherein means are provided for introducing two of the fractions having larger and smaller average particle size respectively into the first elevating means, and wherein means are provided for introducing the third fraction having intermediate average particle size into the second elevating means.

1,825,707 1931 2,542,887. Watson Feb. 20, 1951 1,712,476 Hoppel a a July 5, 1955 

1. APPARATUS FOR CIRCULATING GRANULAR SOLIDS WHICH COMPRISES: MEANS FOR PASSING GRANULAR SOLIDS REPEATEDLY THROUGH A DOWNFLOW SYSTEM AND THROUGH AND UPFLOW SYSTEM COMPREISING AT LEAST TWO SEPARATE ELEVATING MEANS; MEANS FOR CLASSIFYING GRANULAR SOLIDS ACCORDING TO PARTICLE SIZE TO OBTAIN A PLURALITY OF PORTIONS AT LEAST ONE OF WHICH HAS A NARROWER RANGE OF PARTICLE SIZE THAN THE SOLIDS PRIOR TO CLASSIFICATION; MEANS FOR INTRODUCING A SEPARATE PORTION OF THE CLASSIFIED SOLIDS, HAVING NARROWER INTO A FIRST ELEVATING MEANS OF SAID UPFLOW SYSTEM; MEANS FOR INTRODUCING LIFTING GAS INTO THE FIRST ELEVATING MEANS; MEANS FOR DISENGAGING SOLIDS FROM LIFTING GAS AT THE UPPER END OF THE FIRST ELEVATING MEANS; MEANS FOR INTRODUCING DISENGAGED SOLIDS INTO THE DOWNFLOW SYSTEM; MEANS FOR INTRODUCING ANOTHER PORTION OF THE CLASSIFIED SOLIDS INTO A SECOND ELEVATING MEANS OF SAID UPFLOW SYSTEM; AND MEANS FOR INTRODUCING SOLIDS FROM THE SECOND ELEVATING MEANS INTO THE DOWNFLOW SYSTEM. 